A critical component of cellular membranes are phosphoinositides (Pis), lipids containing an inositol head group capable of being reversibly phosphorylated on three different hydroxyl positions to yield an array of signaling molecules. Improper PI metabolism impacts a host of pathological conditions including cancer, diabetes, myotubular myopathy, and Lowe Syndome. The disruption in normal cellular processes embodied in these diseases establishes the crucial role for correct PI maintenance. My study will use the model organism Saccaromyces cerevisiae to dissect the PI4P signaling network and identify novel regulators of PI4P metabolism. In S. cerevisiae, PI4P is produced on the PM by the essential yeast protein Stt4, the yeast homolog of human PI4KIIIa. Subsequently, it is converted to PI(4,5)P2 which impacts various cellular functions ranging from regulation of the actin cytoskeleton to activation of a MAPK pathway. Despite being twice as abundant as PI(4,5)P2, relatively little is know regarding the direct affect of PI4P. Therefore, I plan to focus on the role for this phospholipid on cell dynamics. Initially, using both genetic and biochemical techniques, I will characterize the essential, Stt4-interacting yeast gene YPP1 (YGR198w). YPP1 is a highly conserved gene that has been implicated in both Parkinson's disease and lupus, however, little is known about its function in the cell. Therefore, I will study the interaction between the lipid kinase Stt4 and Yppl. My goal is to determine Yppl's impact on cell viablity, PI4P levels, and activation of Stt4-related pathways. Second, I will identify novel proteins involved in the Stt4 signaling pathway using various genetic screens. Subsequently, I will determine the specific role of these identified genes on PI4P metabolism. Finally, I will characterize the unique organization of lipid kinases into cortical oligomeric signaling platforms: PIK (phosphoinositide kinase) patches. Using fluorsecent-based assays, I will identify the unique features of these structures as well as determine their importance in the cell for regulated PI production. Phosphoinositides are a crossroads for many signaling functions. Accordingly, the disruption of correct PI metabolism impacts a host of cellular processes and is often a hallmark of various diseases. It is essential, therefore, that we understand the basic factors responsible for modulating these crucial signaling pathways. ? ? ?
| Baird, Dan; Stefan, Chris; Audhya, Anjon et al. (2008) Assembly of the PtdIns 4-kinase Stt4 complex at the plasma membrane requires Ypp1 and Efr3. J Cell Biol 183:1061-74 |
